Air spring height measurement arrangement

ABSTRACT

The subject invention relates to an air spring height measurement arrangement comprising a magnetic field transmitting arrangement ( 110 ) and a magnetic field receiving arrangement ( 120 ). The magnetic field transmitting arrangement is adapted to adopt a first state and a second state with regard to the magnetic field receiving arrangement. One of the magnetic field transmitting arrangement ( 110 ) and the magnetic field receiving arrangement ( 120 ) comprises a first coil ( 141 ) and a second coil and the other comprises a third coil ( 143 ). A first central axis ( 161 ) of the first coil and a second central axis ( 162 ) of the second coil enclose a first angle ( 171 ) and, in the first state, a third central axis ( 163 ) of the third coil ( 143 ) and the first central axis enclose a second angle ( 172 ), which first and second angle cannot be 0°.

This application claims benefit of European Patent Application SerialNo. EP 12191149.9, filed on Nov. 2, 2012. The teachings of EuropeanPatent Application EP 12191149.9 are incorporated herein by reference intheir entirety.

FIELD OF THE INVENTION

The invention relates to an air spring height or distance measurementarrangement and an air spring for a vehicle having an air spring heightor distance measurement arrangement.

BACKGROUND OF THE INVENTION

Height or distance measurement has a wide variety of possibleapplications. However, the environment where the height measurement isbeing made can present a wide variety of challenges. This isparticularly the case in situations where height or distancemeasurements are being made in automotive applications. For example, inmeasuring the height of a vehicle frame above the surface of a road,challenges are typically presented by road noise, dirt, dust, andvibrations which are normally present in the environment surrounding thevehicle where the measurement is being taken.

DE 10 2006 017 275 A1 and EP 1845278 A1 describe an air spring having anintegrated positioning device, wherein the distance between two parts ofthe air spring can be measured by an analogue proximity sensor. Commonlyused proximity sensors are, for example, based on an ultrasonicmeasurement principle which is very sensitive in noisy and vibratingenvironments, as the acoustic noise and the ultrasonic measurementprinciple are based on the same physical principle, i.e. soundpropagation. These pneumatic air springs have an integrated heightmeasuring device, a pressure chamber or an inner chamber. The exteriorof the inner chamber is aligned in the analog proximity sensor and ametal plate is arranged opposite to the interior of the proximitysensor. The proximity sensor and the metal plate are formedpre-adjustable to each other.

Further, DE 10 2008 064 647 A1 describes an air spring for a vehiclehaving a measuring device, which measuring device may transmit data andenergy via predetermined and fixed distance contactless. This pneumaticcushioning equipment has a base unit which has a pressure source and avalve unit which has an air supply made of non-metallic material,particularly plastic. A switching valve of the base unit is providedbetween the pressure source and appropriate valve unit of the arrangedair supply.

EP 2 366 972 and United States Patent Publication No. 2012/0056616 A1describe a sensor device for height measurement in an air spring and acorresponding method allowing determining changes in a working stroke ofthe air spring. These publications more specifically disclose a sensordevice for a height measurement, comprising: a transceiving coilarrangement including at least one transceiving coil; a transmittingdrive unit; a receiver unit; a reference coil arrangement; and areference control unit, wherein the transceiving coil arrangement iscoupled to both the transmitting drive circuit and the receiver unit,wherein the reference control unit is coupled to the reference coilarrangement, wherein the reference coil arrangement is movablypositioned with respect to the transceiving coil arrangement, whereinthe drive unit is adapted to drive the transceiving coil arrangementwith an AC power signal of a predetermined duration for generating amagnetic field, wherein the reference control unit is adapted foraccumulating energy out of the generated magnetic field and forgenerating a reference signal based on an amount of the accumulatedenergy, and wherein the receiver unit is adapted for receiving thereference signal and for outputting a signal for determining a distancebetween the transceiving coil arrangement and the reference coilarrangement based on at least one out of a group, the group consistingof the reference signal and the duration of the AC power signal.

SUMMARY OF THE INVENTION

It may be seen as an object of the present invention to provide an airspring height measurement arrangement and an air spring having an airspring height measurement arrangement for distance or height measurementbeing capable of providing more precise height measurement.

The object of the present invention is solved by the subject matter ofthe independent claims, wherein further embodiments are incorporated inthe dependent claims and in the subsequent specification. It should benoted that the following described exemplary embodiments of theinvention apply for the air spring height measurement arrangement aswell as to the air spring.

According to an aspect of the invention, an air spring heightmeasurement arrangement comprises a magnetic field transmittingarrangement and a magnetic field receiving arrangement. The magneticfield transmitting arrangement is adapted to adopt a first state and asecond state with regard to the magnetic field receiving arrangement,wherein one of the magnetic field transmitting arrangement and themagnetic field receiving arrangement comprises a first coil and a secondcoil and wherein the other one of the magnetic field transmittingarrangement and the magnetic field receiving arrangement comprises athird coil. A first central axis of the first coil and a second centralaxis of the second coil enclose a first angle which is unequal to 0°,wherein, in the first state, a third central axis of the third coil andthe first central axis enclose a second angle which is unequal to 0°. Inother words the first angle and the second angle cannot be 0°.

The air spring height measurement arrangement as described above andhereinafter may enable a more precise measurement of a height or adistance between the magnetic field transmitting arrangement and themagnetic field receiving arrangement. In particular, the air springheight measurement arrangement may enable the measurement of a motion ofone of the magnetic field transmitting arrangement and the magneticfield receiving arrangement in more than one dimension, for example amovement of the magnetic field transmitting arrangement towards to oraway from the magnetic field receiving arrangement and a movement in alateral direction with respect to the magnetic field receivingarrangement, respectively.

The magnetic field transmitting arrangement may be adapted to transmit afirst magnetic field and the magnetic field receiving arrangement may beadapted to receive the first magnetic field. The distance between themagnetic field transmitting arrangement and the magnetic field receivingarrangement may thus be determined as a result of the measured intensityof the field lines of the first magnetic field by the magnetic fieldreceiving arrangement.

The first state may correspond to an initial state of the air springheight measurement arrangement, wherein the second state may correspondto a compressed state of the air spring height measurement arrangement,in which compressed state the distance between the magnetic fieldtransmitting arrangement and the magnetic field receiving arrangement isless than in the initial state.

The coils as described above and hereinafter may be coils comprising awounded wire with or without a core (air coils or cored coils), whereinthe core may comprise a ferrite or a ferromagnetic material.

Either the magnetic field transmitting arrangement may have one coil andthe magnetic field receiving arrangement may have two coils or themagnetic field transmitting arrangement may have two coils and themagnetic field receiving arrangement may have one coil.

Each of the coils has a central axis which extends perpendicular ororthogonal with respect to a plane which is determined by the windingsof the coil. In case of a round wounded coil, the central axis extendsorthogonally to the circular shaped cross section of the round woundedcoil.

The first central axis, i.e. the central axis of the first coil, and thesecond central axis, i.e. the central axis of the second coil, intersectunder a first angle unequal to 0°. In other words, the cross sectionarea of the first coil and the cross section area of the second coil areinclined with respect to each other. As a result, the first central axisand the second central axis, of which each is orthogonally with respectto the cross section area of the according coil, intersect under anangle corresponding to the inclination angle between the cross sectionarea of the first coil and the cross section area of the second coil.

In the first state, the first central axis and the third central axis,i.e. the central axis of the third coil, intersect under a second angleunequal to 0°. Thus, the first coil and the second coil as well as thefirst coil and the third coil are arranged such that the respectivecross section area and the respective central axis are inclined to eachother, which means that the first central axis and the second centralaxis on one side as well as the first central axis and the third centralaxis on the other side each have an intersection point in which theenclose the first angle and the second angle, respectively.

Each of the first angle and the second angle may be between 0° and 90°,preferably between 0° and 45° and more preferably between 0° and 20°.For instance, the first angle and the second angle can be within therange of 0.1° to 45° or within the range of 0.5° to 45° or within therange of 1° to 45°. This may allow an air spring height measurementarrangement design with minimum space requirements.

The magnetic field transmitting arrangement and the magnetic fieldreceiving arrangement are arranged with respect to each other in amanner the they move towards each other when the state of the air springheight measurement arrangement changes from the first state to thesecond state and that they move away from each other when the state ofthe air spring height measurement arrangement changes from the secondstate to the first state.

In another embodiment, each of the magnetic field transmittingarrangement and the magnetic field receiving arrangement may comprisetwo coils, wherein at least one of the coils of each of the magneticfield transmitting arrangement and the magnetic field receivingarrangement may be inclined with respect to an intended moving directionof one of the magnetic field transmitting arrangement and the magneticfield receiving arrangement towards the other one. The two coils of themagnetic field transmitting arrangement and the magnetic field receivingarrangement may be arranged opposite to each other, wherein in oneembodiment the coils diagonally opposite to each other are inclinedtowards each other. In one embodiment, one coil of the magnetic fieldtransmitting arrangement and the magnetic field receiving arrangement,respectively, are inclined towards each other and in another embodiment,a first coil of the magnetic field transmitting arrangement is inclinedtowards a second coil of the magnetic field receiving arrangement and asecond coil of the magnetic field transmitting arrangement is inclinedtowards a first coil of the magnetic field receiving arrangement.

In one embodiment, the first coil and the second coil are arrangedopposite to each other with respect to a moving direction of themagnetic field transmitting arrangement or the magnetic field receivingarrangement from the first state to the second state.

According to an embodiment of the invention, the magnetic fieldtransmitting arrangement comprises a magnetic field receiving unit andthe magnetic field receiving arrangement comprises a magnetic fieldtransmitting unit, wherein the magnetic field transmitting arrangementis adapted to transmit a first magnetic field and wherein the magneticfield receiving arrangement is adapted to receive the first magneticfield. The transmitting unit is adapted to transmit a second magneticfield which is generated out of an energy corresponding to the receivedfirst magnetic field and the receiving unit is adapted to receive thesecond magnetic field.

In this embodiment, the distance between the magnetic field transmittingarrangement and the magnetic field receiving arrangement is determinedby measuring the field strength received by the magnetic field receivingunit which is arranged at the magnetic field transmitting arrangement.In other words, the first magnetic field is generated and transmitted bythe magnetic field transmitting arrangement, subsequently detected andits energy stored by the magnetic field receiving arrangement, whereinthe magnetic field transmitting unit of the magnetic field receivingarrangement generates the second magnetic field which is then detectedby the magnetic field receiving unit of the magnetic field transmittingarrangement. Last, the detected magnetic field strength is a measurementcriteria or a value for the distance between the magnetic fieldtransmitting arrangement and the magnetic field receiving arrangement.Thus, the magnetic field receiving arrangement and the accordingmagnetic field transmitting unit may not require an evaluation unit fordetermining the magnetic field strength.

According to a further embodiment of the invention, the first angle isequal to the second angle. In other words, both the second central axisand the third central axis are inclined by the same angle with respectto the first central axis. Thus, in one embodiment the second centralaxis and the third central axis may be parallel to each other and inanother embodiment the second central axis and the third central axismay coincide, i.e. they may extend congruently.

According to a further embodiment of the invention, at least one of thefirst coil, the second coil, and the third coil comprises a coreelement. The core element may bundle or focus the magnetic field linesof the first magnetic field and/or the second magnetic field. Thus, theneeded energy for generating the magnetic fields may be required and theair spring height measurement arrangement as described above andhereinafter may be operated with a minimum of energy.

According to a further embodiment of the invention, the third centralaxis and the second central axis run parallel to each other in the firststate. Thus, the third coil and the second coil are arranged opposite toeach other which may allow an improved measurement accuracy in the firststate or in case the magnetic field transmitting arrangement is arrangeddistant to the magnetic field receiving arrangement.

According to a further embodiment of the invention, the third centralaxis and the second central axis coincide in the first state. Thus, thethird central axis and the second central axis are parallel andcongruent to each other and the third coil and the second coil arealigned to each other in a manner that in the first state the crosssection areas of these coils are parallel to each other.

When being subjected to a movement from the first state to the secondstate, the third coil may be moved along the first central axis, i.e.towards to or away from the first coil. In this case, the inclinationangle of the second central axis with respect to the third central axisdoes not change but they may not be congruent to each other.

By the individual inclination angle of the coils with respect to eachother, an air spring height measurement arrangement as described aboveand hereinafter may thus enable a more precise distance measurementbetween the magnetic field transmitting arrangement and the magneticfield receiving arrangement and furthermore may facilitate a measurementof a lateral movement of one of the magnetic field transmittingarrangement and the magnetic field receiving arrangement with respect tothe other one.

Furthermore, the air spring height measurement arrangement mayfacilitate the elimination of measurement errors as in a more distantstate of the magnetic field transmitting arrangement and the magneticfield receiving arrangement, the third coil and the second coil, whosecentral axes coincide or are located close to each other, may provide amore exact measurement and in a closer state of the magnetic fieldtransmitting arrangement and the magnetic field receiving arrangement,the third coil and the first coil, which are arranged opposite to eachother in a moving direction from the first state to the second state,may provide a more exact measurement.

Thus, the air spring height measurement arrangement as described aboveand hereinafter may be tolerant, and in particular fault-tolerant, withrespect to lateral movements of one of the magnetic field transmittingarrangement and the magnetic field receiving arrangement with respect tothe other one due to vibrations or other force impacts as one of themagnetic field transmitting arrangement and the magnetic field receivingarrangement comprises two coils.

According to a further embodiment of the invention, the first coilcomprises a lateral offset in a direction perpendicular to the firstcentral axis with regard to the second coil. The first coil and thesecond coil are arranged such that they are displaced in order to have agap or a spacing in between them. In other words, the first coil and thesecond coil neither adjoin nor overlap each other. The lateral offset isthe distance between the first coil and the second coil.

According to a further embodiment of the invention, the first coiloverlaps the second coil at least partially in a direction perpendicularto the first central axis. Thus, the air spring height measurementarrangement may allow a space saving arrangement of the first coil andthe second coil.

According to a further embodiment of the invention, the first coilcompletely overlaps the second coil in a direction perpendicular to thefirst central axis. In particular, the cross section area of the firstcoil may be larger than the cross section area of the second coil. Thus,the second coil may especially be arranged within the windings of thefirst coil.

An overlap of the first coil and the second coil may be an overlap withregard to the third coil, i.e. one of the first coil and the second coilis behind the other one with respect to a moving direction of the thirdcoil towards the first coil and the second coil.

According to a further embodiment of the invention, the third coil isadapted to move along the first central axis when being moved from thefirst state to the second state. The accuracy and precision of thedistance measurement over a large movement distance or measurement rangemay be improved by moving the third coil towards to and away from thefirst coil along the first central axis while at the same time the thirdcoil and the third central axis is inclined towards the second coil.

According to a further embodiment of the invention, each of the firstcoil and the second coil is a printed coil on a printed circuit board.This may further reduce the space needed for installing an air springheight measurement arrangement. The first coil and the second coil maybe designed as conducting paths on a printed circuit board (PCB) or on aprinted wiring board.

In one embodiment, the first coil and the second coil may be arrangedeach on an individual PCB. This allows an inclined arrangement of thefirst coil with respect to the second coil.

In an alternative embodiment, the first coil and the second coil may bearranged on a single PCB, wherein the PCB comprises a bending area whichallows an inclined arrangement of one of the first coil and the secondcoil with respect to the other one.

According to a further embodiment of the invention, the third centralaxis and the first central axis run parallel to each other in the secondstate.

Thus, the third coil and the first coil are arranged opposite to eachother in the second state, i.e. when the magnetic field transmittingarrangement and the magnetic field receiving arrangement are close toeach other, such that a measurement accuracy may be increased when oneof the magnetic field transmitting arrangement and the magnetic fieldreceiving arrangement is close the second state.

According to a further embodiment of the invention, the third coil andthe second coil are arranged opposite to each other in a direction of asecond measuring direction in the first state.

The receiving coils or the magnetic field receiving arrangement mayprovide the highest sensitivity to changes of the distance between themagnetic field transmitting arrangement and the magnetic field receivingarrangement when the according coil is arranged such that a direction ofthe first magnetic field and/or the second magnetic field corresponds tothe alignment of the receiving coil and is arranged such that thereceiving coil is subjected to the highest field strength. The measuringdirection is defined by the arrangement of the coils opposite to eachother and by the direction of detecting changes in the received magneticfield strength when moving one of the coils away from and towards to theother one of the coils.

In case the coils are designed as air coils, this means that a crosssection area of the third coil and of the second coil, respectively, arearranged parallel to each other and the respective central axescoincide. In case the coils are designed as cored coils, the secondcentral axis and the third central axis are parallel to each other, andthe coils do not have a longitudinal offset in a direction along any oneof these axes, and when starting a movement of any one of the third coiland the second coil in the first state, the third coil and the secondcoil are being moved directly towards each other.

According to a further embodiment of the invention, the third coil andthe first coil are arranged opposite to each other in a direction of afirst measuring direction in the second state. Thus, the third coilchanges its orientation in space when being moved from the first stateto the second state. This may in particular occur while a swing movementof the third coil. The remarks with regard to the orientation of thethird coil and the second coil in the first state apply in an analogousmanner to the orientation of the third coil and the first coil in thesecond state.

According to a further embodiment of the invention, a movement of themagnetic field transmitting arrangement from the first state to thesecond state is adapted to occur within a measuring plane which isdefined by the first measuring direction and the second measuringdirection. The measuring plane is thus held by the vectors of the firstmeasuring direction and the second measuring direction.

According to another aspect of the invention, an air spring for avehicle is provided which comprises a first mounting element for beingfixed to one of a vehicle's chassis and a movable part of a vehiclebeing movable with respect to the chassis, a second mounting element forbeing fixed to the other one of the vehicle's chassis and the movablepart of the vehicle being movable with respect to the chassis, a bellowextending from the first mounting element to the second mounting elementand including an air volume, and an air spring height measurementarrangement as described above and hereinafter. The magnetic fieldtransmitting arrangement is arranged at the first mounting element andthe magnetic field receiving arrangement is arranged at the secondmounting element, wherein a movement of the first mounting element withrespect to the second mounting element represents at least a part of aworking stroke of the air spring.

The air spring with the air spring height measurement arrangement asdescribed above and hereinafter may in particular be adapted to measurea road condition and a vehicle condition due to vibrations or cargorestrictions.

The invention relates to measuring the distance between two locations,like between the upper body of a vehicle and the wheel-suspension, orlike between the chassis of a truck or trailer and the wheel axle.However, the air spring height measurement arrangement as describedabove and hereinafter can be used and applied to applications where thedistance to be measured can be as little as 1 mm or as large as 1 meter.

The measurement principle is based on low field-strength, magneticphysics. The benefit of using low magnetic field strengths are lowelectric power consumptions, reduced magnetic emissions to eliminate therisk of interfering with other systems placed nearby, and eliminatingthe possibility that magnetic particles may be attracted to thismeasurement solution (cannot clot-up with ferromagnetic particles of anykind).

One of the targeted applications (the transportation market) may requirethat the air spring height measurement arrangement has to be very rugged(particular when placed near or at a suspension system). For instance,the air spring height measurement arrangement typically must be ruggedenough to function reliably reliable under very harsh operatingconditions including operating temperatures which are within a widerange from as low as about −50° C. to as high as about 125° C., exposureto oil vapor, humidity, dust and dirt, and mechanical shocks andvibrations. In other words, the arrangement (height measuring devise orsystem) should be relatively insensitive to changes in temperature,insensitive to mechanical shocks and vibrations, as well as beingcapable of operating reliably under conditions of exposure to highhumidity, oil vapor, dirt, and/or dust.

However, it has to be recognized that the limiting factor in relation tothe sensor system ruggedness may always be what the sensor electronicscan cope with. Therefore, it may be important that the actual sensormodule (the physical sensing element) can be placed separately inrelation to the required sensor electronics, which is here the case.Meaning that the electronics could be placed at a location that is notexposed too very harsh operating conditions, while the actual sensingelement is exposed to it.

To avoid unwanted interferences with commercially available radioreceivers (car radios, mobile phones, television sets, remote controls,etc.), the operational frequency of the height or distance sensorarrangement as described above and hereinafter may be limited to maximum100 kHz and may be 50 kHz in one preferred embodiment. The sensor systemmay perform better when choosing a higher frequency (like 300 kHz oreven near 1 MHz) but then the required magnetic shielding may bedifficult to achieve and because of the required additional EMI (ElectroMagnetic Interference) control the overall system cost may growsignificantly. This may be one of the main reasons of the specificationschosen for the inductors used (physical dimensions and inductivity).

The air coils may have a diameter between 8 and 20 cm, wherein thedistance between the magnetic field transmitting arrangement and themagnetic field receiving arrangement in the first state may correspondto the twofold to fivefold air coil diameter.

The core of the cored coils may have a diameter of between 1 mm and 10mm and a length of 2 mm to 6 mm, wherein the coils may have between 100and 400 windings.

The diameter of the air coils may determine the practical usablemeasurement range of the height measurement arrangement. In connectionwith an air spring, the measurement range may also be called: theworking stroke of the air spring or an according wheel suspension.

The main benefit of using air coils may be that the height and distancesensor system may be relatively insensitive to a range of tolerances andoperational conditions. This includes that metallic objects (conductivemetals and ferromagnetic metals) are placed near the side of the airspring height measurement arrangement.

The main benefit of using inductors (coils) with ferro-property relatedcore material may be that they can be built much smaller to achieve asimilar measurement performance in comparison to the much larger aircoils. However, coils with ferro-core material may be by far moresensitive to ferro-metallic objects placed nearby and to mechanicalassembly tolerances (like tilting, for example).

The present invention more specifically describes an air spring heightmeasurement arrangement (100), comprising a magnetic field transmittingarrangement (110); and a magnetic field receiving arrangement (120);wherein the magnetic field transmitting arrangement is adapted to adopta first state and a second state with regard to the magnetic fieldreceiving arrangement; wherein one of the magnetic field transmittingarrangement (110) and the magnetic field receiving arrangement (120)comprises a first coil (141) and a second coil (142); wherein the otherone of the magnetic field transmitting arrangement (110) and themagnetic field receiving arrangement (120) comprises a third coil (143);wherein a first central axis (161) of the first coil and a secondcentral axis (162) of the second coil enclose a first angle (171) whichis unequal to 0°; and wherein, in the first state, a third central axis(163) of the third coil (143) and the first central axis enclose asecond angle (172) which is unequal to 0°.

The present invention further describes an air spring (300) for avehicle, comprising a first mounting element (310) for being fixed toone of a vehicle's chassis (230) and a movable part (220) of a vehiclebeing movable with respect to the chassis; a second mounting element(320) for being fixed to the other one of the vehicle's chassis and themovable part (220) of the vehicle being movable with respect to thechassis; a bellow (330) extending from the first mounting element to thesecond mounting element and including an air volume; an air springheight measurement arrangement (100) according to any one of thepreceding claims; wherein the magnetic field transmitting arrangement(110) is arranged at the first mounting element; wherein the magneticfield receiving arrangement (120) is arranged at the second mountingelement; and wherein a movement of the first mounting element withrespect to the second mounting element represents at least a part of aworking stroke (130) of the air spring.

These and other aspects of the present invention will become apparentfrom and elucidated with reference to the embodiments describedhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described in thefollowing with reference to the following drawings.

FIG. 1A illustrates a distance measurement arrangement.

FIG. 1B illustrates a distance measurement arrangement.

FIG. 1C illustrates a distance measurement arrangement.

FIG. 1D illustrates a signal pattern of a distance measurementarrangement.

FIG. 1E illustrates a distance measurement arrangement.

FIG. 2 illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 3 illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 4 illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 5 illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 6 illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 7 illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 8 illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 9 illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 10 illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 11A illustrates a distance measurement arrangement.

FIG. 11B illustrates a distance measurement arrangement.

FIG. 12 illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 13 illustrates a signal pattern of an air spring height measurementarrangement according to an exemplary embodiment of the invention.

FIG. 14 illustrates a magnetic field receiving arrangement for an airspring height measurement arrangement according to an exemplaryembodiment of the invention.

FIG. 15A illustrates a distance measurement arrangement.

FIG. 16 illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 16A schematically illustrates an air spring height measurementarrangement according to an exemplary embodiment of the invention.

FIG. 17A illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 17B illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 17C illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 18A illustrates a bottom plate of an air spring.

FIG. 18B illustrates a bottom plate of an air spring according to anexemplary embodiment of the invention.

FIG. 19 illustrates an air spring height measurement arrangementaccording to an exemplary embodiment of the invention.

FIG. 20A illustrates a magnetic field receiving arrangement for an airspring height measurement arrangement according to an exemplaryembodiment of the invention.

FIG. 20B illustrates a magnetic field receiving arrangement for an airspring height measurement arrangement according to an exemplaryembodiment of the invention.

FIG. 21A illustrates an air spring with an air spring height measurementarrangement according to an exemplary embodiment of the invention.

FIG. 21B illustrates an air spring with an air spring height measurementarrangement according to an exemplary embodiment of the invention.

FIG. 22 illustrates a wheel suspension with an air spring according toan exemplary embodiment of the invention.

FIG. 23 illustrates a wheel suspension with an air spring according toan exemplary embodiment of the invention.

The reference numerals used in the drawing are as follows:

-   -   100 air spring height measurement arrangement    -   105 power supply    -   110 magnetic field transmitting arrangement    -   111 transmitter circuit    -   112 transmitted signal    -   120 magnetic field receiving arrangement    -   121 receiver circuit    -   122 received signal    -   124 signal threshold value    -   126 encoded received signal    -   127 duration of encoded received signal    -   130 measuring distance    -   131 first measuring direction    -   132 second measuring direction    -   140 coil    -   141 first coil    -   142 second coil    -   143 third coil    -   145 lateral offset    -   146 overlap section    -   151 first core    -   152 second core    -   153 third core    -   161 first central axis    -   162 second central axis    -   163 third central axis    -   165 symmetry line    -   171 first angle    -   172 second angle    -   181 first magnetic field    -   182 second magnetic field    -   190 printed circuit board    -   195 bending line    -   210 mounting plate    -   220 movable part    -   221 hinge    -   225 moving direction    -   230 vehicle's chassis    -   300 air spring    -   310 first mounting element    -   320 second mounting element    -   330 bellow

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1A, 1B, and 1C illustrate a height measurement arrangement 100,each comprising a magnetic field transmitting arrangement 110 and amagnetic field receiving arrangement 120, wherein each of the magneticfield transmitting arrangement and the magnetic field receivingarrangement are illustrated in form of a coil 140. The coil may be anair coil as shown in FIGS. 1A, 1B, and 1C (magnetic field transmittingarrangement only), or a cored coil as shown in FIG. 1C in connectionwith the magnetic field receiving arrangement 120, which comprises acore 150.

The coils of the magnetic field receiving arrangement and of themagnetic field receiving arrangement may be arranged such that the crosssectional areas of the coils are parallel to each other and themeasuring distance is in between the cross section areas, i.e. the coilsare moving towards each other, as shown in FIGS. 1A and 1C, or such thatthe cross section areas of the coils are in the same plane, i.e. thecoils are moving along a plane defined by the cross sectional areas ofthe coils when moving away from or towards each other and the measuringdistance is arranged in the same plane.

When using air coils then they may have to be placed parallel to eachother to provide improved measurement performances. FIG. 1A mayrepresent the more reliable distance measurement system in comparison toFIG. 1B, which illustrates another potentially possible solution.

The larger the diameter of the air coil, the larger the measurementrange may be. Depending on the sensitivity of the magnetic fieldreceiving arrangement, the practical measurement range may vary betweentwo to five times of the transmitter air coil diameter. For example whenchoosing a transmitter air coil diameter of 100 mm, then the practicalmeasurement range (maximum distance between the transmitter and receivercoil) may be in the range of 200 mm and 500 mm. Accordingly, thepractical measurement range will typically be about 2 times to about 5times the diameter of the transmitter air coil.

FIG. 1C illustrates an air spring height measurement arrangement whichmay achieve good measurement results when using a large air coil as themagnetic field transmitting arrangement and a cored coil withferro-material core that can be built much smaller than the air coil, asmagnetic field receiving arrangement. This design may be tolerant totilting tolerances, but may have the disadvantage that the receivingcoil and in particular the core has to stand up-right, i.e. with itslongitudinal axis parallel to the measuring direction 130. Thus, thelarger the core item is, the shorter the usable working stroke of theair spring height measurement arrangement may be. From this point ofview it may be best to have a very short core item in the magnetic fieldreceiving arrangement, which on the other side may reduce thesensitivity range of the magnetic field receiving arrangement.

Coils with cores or inductors with a ferromagnetic material core may beused in order to reduce the physical dimension of the inductors (coils)used to build an air spring height measurement arrangement (or distancesensor). Such inductors or coils may be built with a much smallerdiameter (in comparison to air coils), which may also have positiveeffects on the overall material cost when building an air spring heightmeasurement arrangement.

FIG. 1D illustrates a transmitted signal 112 with four signal sequences112A, 112B, 112C, and 112D transmitted by the magnetic fieldtransmitting arrangement. Corresponding to the transmitted signals, thereceived signal 122 with the signal sequences 122A, 122B, 122C, and 122Dare illustrated.

The distance between the magnetic field transmitting arrangement and themagnetic field receiving arrangement is determined as a result of thepulse length 127A, 127C of the encoded received signals 126A, 126B,126C, and 126D. The pulse length is determined measured between thepoints in time where the received signal 122 is higher than apredetermined signal threshold value 124. In general, the closer themagnetic field transmitting arrangement and the magnetic field receivingarrangement are to each other, the longer is the pulse length 127, asthe energy received from the detected magnetic field is higher incomparison to a larger distance between the magnetic field transmittingarrangement and the magnetic field receiving arrangement.

Instead of using a continuously transmitted signal, emitted by themagnetic field transmitting arrangement (no signal interruptions orsignal pauses of any kind), the transmitted signal can be a simple burstof one or a few signal wave shapes of a constant frequency. The chargingtime and the discharging time of the receiving oscillator is then thebasis for the determination of the distance of the magnetic fieldreceiving arrangement to the magnetic field transmitting arrangement.

The closer the transmitter coil is placed to the receiver coil (orreceiver coils) the longer the charge/discharge time of the receivedsignal will be. The transmitter is emitting short signal bursts of agiven frequency. FIG. 1D illustrates a change in the distance from themagnetic field receiving arrangement to the magnetic field transmittingarrangement from “short” distance (A), gradually with every followingtransmitter signal burst (B, C, D) to a large distance (D). As thedistance between the transmitter coil and the receiver coil isincreasing, the signal received at the receiver coil will becomesmaller.

Using a programmable signal amplitude threshold detection level 124allows the following electronics circuitry to determine the time for thereceived signal to discharge. In the example shown in FIG. 1D, thesignal discharging-time will begin to count from the moment the receivedsignal crosses the programmable threshold line. Other solutions arepossible as well. The signal discharging time will be longer (A) whenthe spacing between the transmitter coil and the receiver coil is veryshort. As the spacing is increasing (C) the discharging time will becomeshorter. The pulse length will be an indication of the spacing betweenthe two coils.

The reason for using a “programmable” receiver threshold level 124 (orvoltage) may be to increase the sensitivity of the receiver system andto deal more easily when the signal noise may increase. Of course, theabove shown solution will also work when using a “fixed” levelthreshold.

The key benefit of this signal decoding concept may be that with littleeffort and little current, larger distances can be measured. Such asolution may have the potential of emitting signals that will interferewith other electronic systems that are placed nearby (potentially highEMI emissions).

FIG. 1E illustrates an air spring height measurement arrangement 100with a magnetic field transmitting arrangement 110 and a magnetic fieldreceiving arrangement 120, wherein the magnetic field transmittingarrangement comprises a third coil 143 and the magnetic field receivingarrangement comprises a first coil 141 and a second coil 142, which areall air coils. Each coil has a central axis 161, 162, and 163,respectively, wherein the first central axis 161 and the third centralaxis 163 coincide and the second central axis is parallel to the firstand the third central axis.

Such an arrangement may enable a differential measurement of signals,i.e. the transmitted magnetic field of the magnetic field transmittingarrangement may be received and detected by both of the first coil 141and the second coil 142 of the magnetic field receiving arrangement 120.Thus, a more precise distance measurement may be provided.

FIG. 2 illustrates an air spring height measurement arrangement 100wherein the second central axis 162 and the third central axis 163 areinclined with respect to the first central axis 161. In this particularembodiment, the second central axis 162 and the third central axis 163coincide such that both of the axes 162 and 163 enclose a first angle171 and a second angle 172, respectively with the first central axis.

In other words, the third coil 143 is inclined towards the second coil142 and the second coil 142 is inclined towards the third coil 143,wherein the measuring distance 130 and the moving direction of the thirdcoil 143 is along the first central axis 161 towards and away from thefirst coil 141.

The effect about the differential signal can be altered and changed byslightly tilting the transmitter coil 143 towards the receiver coil 142.The absolute received signal strengths may be increased when thetransmitter and receiver coils are facing each other (placed parallel toeach other and/or having coinciding central axes).

In some applications it may not be possible to use the “tilted” coilplacement (for space or cost reasons, for example). In such a case, thesensor is still fully functional but the achievable sensor performancemay be somewhat limited compromised. “Tilting” the coils will increasethe sensor measurement range and allows to achieve a more linear sensoroutput signal before the potentially used electronic digital signalprocessing stage.

In this embodiment, the signal received at the coil 141 may be largerthan from the coil 142 in FIG. 1E. When tilting the transmitter coil 143and the receiving coil 142 towards each other as shown in FIG. 2, thesignal received in coil 142 may increase and the signal received in coil141 may decrease.

The first angle 171 and the second angle 172 may vary between differentdesign forms of the air spring height measurement arrangement. The firstangle may be different from or identical with the second angle.

FIG. 3 illustrates an embodiments of the air spring height measurementarrangement 100, wherein the second central axis 162 and the thirdcentral axis 163 are arranged parallel to each other and do notcoincide. The second central axis 162 encloses a first angle 171 withthe first central axis 161 and the third central axis 163 encloses asecond angle 172 with the first central axis 161. Furthermore, the firstcoil 141 and the second coil 142 are arranged such that they are spacedapart laterally comprising a lateral offset 145 in between them.

The measurement signal obtained by each of the receiver air coils 141,142 may be processed individually (absolute measurements of the signalsobtained from first coil 141 and second coil 142) which is called heretriangulation mode, or a differential mode signal processing approachcan be used. In the differential mode sensor design only the differencein the received signal of the first coil 141 and the second coil 142 isof importance. The receiver circuits and the immediate following signalprocessing electronics may look very different when comparing thetriangulation mode with the differential mode sensor design. However, inboth cases the physical placement and the design of the air coils may besimilar or identical.

In FIG. 3, one signal transmitting coil 143 and two signal receivingcoils 141, 142 are used. In order to achieve the maximal working strokeof an air spring, the two receiving coils are placed within the same“plane” (meaning that the receiver coils are not placed on top of eachother with some spacing between them, i.e. without an overlappingsection).

By placing the two receiver coils 141, 142 side by side, and by aligningthe centre of the transmitter coil 143 with one of the receiver coils(in this example with the first coil 141), the differential receivercoils signal strength and the linearity of the resulting sensor outputsignal may be a function of a number of parameters: distance between thetransmitter and the receiver coils (limits about the maximum distancebetween the transmitter and receiver coils may apply), inclinationangles of one or more coils in relation to each other, spacing (measuredfrom the geometric centre of one receiver coil 141 to the geometriccentre of the other receiver coil 142) between the two receiver coils,chosen path of movement between the receiver coils and transmitter coil(on a straight line to each other, or in an arc-shaped curve which willbe described later on), design symmetry of the receiver coils 141, 142(symmetry means that the coils are identical).

FIG. 4 illustrates an air spring height measurement arrangement whereinthe first coil 141 and the second coil 142 overlap partially in anoverlap section 146.

FIG. 5 illustrates an air spring height measurement arrangement whereinthe first coil 141 completely overlaps the second coil 142, i.e. thesecond coil 142 has a cross section area smaller than the cross sectionarea of the first coil 141.

FIGS. 6, 7, and 8 illustrate the motion of the third coil 143 towardsthe magnetic field receiving arrangement 120 with the first coil 141 andthe second coil 142 along the first central axis 161, wherein theinclination angle of the third coil 143 with respect to the firstcentral axis 161 remains constant, i.e. the third central axis 163remains parallel to the second central axis 162 during the movement ofthe third coil 143 along the first central axis 161.

The transmitter coil 143 is moving towards the receiver coil 141 on adirect path: first central axis 161. FIG. 6 shows the air spring heightmeasurement arrangement in the first state, wherein the third centralaxis 163 coincides with the second central axis 162. The greater thedistance is between the transmitter coil and the receiver coils (till apredetermined maximum distance has been reached), the better thesymmetrical alignment will be between coil 143 and coil 142. The shorterthe distance is between coil 143 and coil 141 the better the signaltransfer between the two coils 143 and 141. At the same time (when coil143 is moving towards coil 141) the transmitting coil 143 is leaving thesecond central axis 162 (which leads to the geometric center of coil142).

While the signals received by the two coils 141 and 142 will initiallyincrease (as coil 143 is moving towards coil 141), the curves thatdescribe the “Distance/Signal Gain” will be different for coil 141 andcoil 142. These differences in the two “signal gain versus distance”curves is the actual sensor output signal. By changing the first angleand the second angle, the differential signal curve (sensor outputsignal=signal coil 141−signal coil 142, for example) can be influencedand changed.

To have better control about the optimal measurement distance (betweenthe transmitter and receiver coils) the receiver coils can be placedside-by-side having a lateral offset (as shown in FIG. 3), or canoverlap each other (as shown in FIGS. 4, 6 to 8) or can be placed insideeach other (as shown in FIG. 5).

To avoid unwanted effects which may arise due to overlapped receivercoil wires, one of the receiver coils can be stretched, towards an ovalshape. The diameter of one receiver coil may be much smaller and may beplaced off-centre in relation to the other receiver coil. Placing thecoils “inside each other” may have an advantage when manufacturing thecoils, in particular when using a PCB (printed circuit board) coildesign.

Another benefit may be that the receiver coil 141 can have a very largediameter which may result in larger signal amplitude. In this case,additional measures may be necessary to avoid that the two receivingcoils begin to influence each other.

FIGS. 9 and 10 illustrate that the third coil 143 on the one hand aswell as the first coil 141 and the second coil 142 on the other hand maybe adapted to form either the magnetic field transmitting arrangement orthe magnetic field receiving arrangement. Further, any one of the thirdcoil 143 or the first coil 141 and the second coil 142 may be adapted tomove towards the other one.

In other words, each of the magnetic field transmitting arrangement andthe magnetic field receiving arrangement may comprise one or more coils,wherein each of the coils may be inclined with respect to the othercoils or a given moving direction of either the magnetic fieldtransmitting arrangement or the magnetic field receiving arrangement.

FIGS. 11A and 11B illustrate an air spring height measurementarrangement 100 similar to the air spring height measurement arrangementillustrated in FIGS. 1A and 1E, respectively, wherein for generalremarks reference is made to these FIGS.

In contrary to FIGS. 1A and 1E, FIGS. 11A and 11B show the usage ofsmall dimension flux gate sensors as first coil 141 and second coil 142,each having a core 151, 152.

FIG. 11B shows the third coil 143 in a first state (see position 143A)and in a second state (see position 143B).

FIG. 12 shows an air spring height measurement arrangement 100 similarto the air spring height measurement arrangement shown in FIG. 3,wherein the first coil 141 and second coil 142, each having a core 151,152, are designed as small dimension flux gate sensors.

The receiving coils 141, 142 may be replaced by very small dimensionflux gate circuits, for example. One obvious benefit may be the reducedspace requirements. Another benefit may be the very high magnetic fieldsensitivity such a design solution offers and with this the opportunityto extend the practical measurement range, i.e. the measuring distance130. A flux gate circuit may require its own electronics.

The air spring height measurement arrangement may be built using onlyone flux gate coil (as shown in FIG. 11A), or using more than oneMagnetic Field Sensing (MFS) inductor (see FIGS. 11B, 12). When usingmore than one MFS inductor, it is possible to use a differential modesignal processing mode as described above.

In general, all the coils as described above and hereinafter may be aircoils, cored coils or small dimension flux gate circuits.

In general, the magnetic field transmitting arrangement generates andtransmits a magnetic field which is received by the magnetic fieldreceiving arrangement. By the strength of the magnetic field received bythe magnetic field receiving arrangement, the distance between themagnetic field transmitting arrangement and the magnetic field receivingarrangement is determinable.

In an alternative embodiment, the magnetic field receiving arrangementmay be adapted to receive the first magnetic field and generate a secondmagnetic field whose intensity corresponds to the energy received by thefirst magnetic field. The second magnetic field may then be received bya receiver unit of the magnetic field transmitting arrangement and thenbe used in order to determine the distance between the magnetic fieldtransmitting arrangement and the magnetic field receiving arrangement.

FIG. 13 illustrates the received signals 122A, 122B used for determiningthe distance between the magnetic field transmitting arrangement and themagnetic field receiving arrangement using the differential mode. Thesignals 122A and 122B may be generated and transmitted by twotransmitting coils, as shown in FIG. 10.

The two transmitting coils could be driven by one and the same signalgenerator circuit. When deciding to do so then it is important toalternate the transmitting signal sequence between the two transmittingcoils. Meaning that only one transmitter coil will be powered by thesignal generator (either the first or the second, but not bothtogether). The alternating signal transmitting sequence may have thebenefit of reducing unwanted parasitic effects, like signalinterferences between the two transmitter coils.

The receiver signal decoding may be easier and of higher quality whenusing alternating transmitter signal. Meaning that only one transmittercoil will be active at any given time. One benefit may be that one andthe same transmitter frequency will be used which simplifies thereceiver filter circuitry substantially (which may result in smallercircuit board, lower costs).

Alternatively, two different frequencies can be used to drive the twotransmitting coils. This way both transmitting coils can be activesimultaneously. By doing so, the sensor signal bandwidth (SBW) will bedoubled (the air spring height measurement arrangement may becomefaster), but the required receiver electronics now has to differentiatereliably between the two transmitter frequencies. This may result in amore complex receiver electronics design.

FIG. 14 illustrates magnetic field receiving arrangement 120 in form ofa printed circuit board 190 having a first coil 141 and a second coil142, each in form of printed paths on the printed circuit board.

The printed circuit board 190 comprises a flexible part in form of abending line 195 which enables the setting or adjustment of aninclination angle of one of the first coil and the second coil withrespect to the other one of the coils 141, 142.

In other words, instead of using single-wire wounded coils, it is alsopossible to use PCB-printed coils. Using PCB-printed coils may have acost advantage when the physical coil dimensions are relative small. Inaddition, PCB-Printed coils may be protected much better from unwantedeffects when using them under harsh operating conditions. From a certainlarger size onwards, the effects when using PCB-printed coils mayoutweigh the other features (higher costs, larger impedance, and unusedPCB space).

A PCB coil may be realized with a single layer design (only using thecopper material on one side of the PCB) or with a multilayer PCB (usingcopper layers on both sides and even using layers that are sandwichedbetween the two outer layers of a PCB. To a certain extent it may bepossible to place some electronics components “inside” the center of thePCB design coil (center means: the otherwise empty space in the middleof the PCB coil). However, the higher the amount of conductive materialthat will be placed in the center of the coil, the stronger unwantedinterferences may become. This may be even more so when the componentsconsist of ferromagnetic material.

FIG. 15A illustrates an air spring height measurement arrangement 100comprising a first coil 141 and a second coil 143 which are arrangedopposite to each other in relation to a measuring direction 130 whichcorresponds to the moving direction of the third coil 143. The thirdcoil 143 is illustrated in the first state (the more distant positionwith respect to the first coil) and in the second state (the closerposition with respect to the first coil). The movement of the third coiltowards and away from the first coil corresponds to the distance changesto be measured. The distance between the third coil 143 and the firstcoil 141 is determined based on the field strength of the first magneticfield 181 detected by the first coil 141, wherein the field lines of thefirst magnetic field are illustrated schematically having their sourceand sink at the third core 153.

The first coil 141 has a first core 151 and the third coil 143 has athird core 153, wherein the central axis of the first coil and the thirdcoil, i.e. a longitudinal extent of the first core and of the thirdcore, respectively, run parallel to each other.

The air spring height measurement arrangement 100 illustrated in FIGS.1A to 12 is formed such that the measuring direction 130 and themovement direction of one of the magnetic field transmitting arrangementand the magnetic field receiving arrangement is along the magnetic fieldlines of the generated first magnetic field, wherein in the embodimentillustrated in FIG. 15A, the measuring direction 130 and the movementdirection of one of the magnetic field transmitting arrangement and themagnetic field receiving arrangement or the first coil and the thirdcoil, respectively, is transverse or orthogonal to the magnetic fieldlines of the first magnetic field.

The transmitter coil 143 and the receiver coil 141 are placed inparallel to each other in order to achieve a large measurement range130. The magnetic field lines 181 emanating from the transmitter coil143 are reaching out in all directions. This sensor design may be moresensitive to metallic and conductive objects that are placed within thereach of the shown flux lines. The flux lines reaching out towards thereceiver coil 141 will be called the working field, the interfering fluxlines or the field losses are called here loss field.

To reduce the sensors sensitivity towards other ferromagnetic objectsand conductive objects, that may be placed close to the air springheight measurement arrangement, either the loss field may have to beblocked, e.g. through passive magnetic shielding, or an activecompensation approach, which will be described further below, may haveto be applied. Without any of these two compensation design options,this specific sensor design may have a limited use and may be suitablefor specific applications only.

FIG. 16 illustrates an air spring height measurement arrangement 100with a magnetic field transmitting arrangement 110 having a third coil143 and a magnetic field receiving arrangement 120 having a first coil141 and a second coil 142, wherein each of the coils is a cored coil.

The third coil 143 is attached to a movable part 220, which is rotatablymovable in the moving direction 225 around the hinge 221. The third coil143 and the movable part 220 are shown in the first state indicated bythe suffixes “A” to the respective reference signs and in the secondstate indicated by the suffixes “B” to the respective reference signs.

In the first state, the third coil 143A is located opposite to thesecond coil 142 and the respective central axes 163, 162 (not shown) areparallel to each other. In the second state, the third coil 143B islocated opposite to the first coil 141 and the respective central axes163, 161 are parallel to each other.

Thus, the measurement accuracy may be high in a position of the movablepart close to the first state as the third coil and the second coil arearranged opposite to each other and in a position of the movable partclose to the second state as the third coil and the first coil arearranged opposite to each other such that the sensitivity of the coils141, 142 of the magnetic field receiving arrangement 120 may be maximumeven though the movable part is subjected to a rotary movement.

The relation of the respective central axes of the coils in the airspring height measurement arrangement illustrated in FIG. 16 will becomemore apparent from the illustration shown in FIG. 16A below.

In applications where a wheel suspension system is “swinging”in-and-out, i.e. is performing a rotary movement or following anarc-shaped curve, a tilted receiver coil 142 may be most sensitive whenthe transmitter coil 143 is in a parallel aligned position 143A. Whenanalyzing the signal from both receiver coils 141 and 142, then acomputation device like a microprocessor based system can calculate theexact distance and angular movement of the third coil 143 and themovable part 220.

FIG. 16A illustrates the central axes and the angles in between thecentral axes of the coils in the air spring height measurementarrangement 100 shown in FIG. 16.

In the first state, the third central axis 163A of the third coil 143Aruns parallel to the second central axis 162 of the second coil 142.Further, in the first state, the third central axis 163A and the firstcentral axis 161 intersect under the second angle 172 and the secondmeasuring direction 132 extends perpendicular to the third central axis163A and to the second central axis 162 between the axes 163A and 162.

In the second state, the third central axis 163B runs parallel to thefirst central axis 161 and intersects with the second central axis 162under the first angle 171. Furthermore, the first central axis 161 andthe second central axis are aligned with respect to each other such thatthey enclose the first angle 171 and the first measuring direction 131extends perpendicular to the third central axis 163B and to the firstcentral axis 161 between the axes 163B and 161.

It should be noted that, in the first state, the third central axis 163Aand the second central axis 162 may also intersect, i.e. not runparallel to each other. Similarly, in the second state, the thirdcentral axis 163B and the first central axis 161 may intersect.

FIGS. 17A, 17B, and 17C illustrate different options of signalconditioning or signal processing and power supply of the air springheight measurement arrangement 100 according to the invention.

The transmitter side and the receiver side of the air spring heightmeasurement arrangement require electronics. The required electronicscan be placed on one common PCB (transmitter and receiver electronicsare placed together) or can be on separate PCBs. This will result indifferent wiring options.

FIG. 17A illustrates a common power supply 105 and separate signalcondition and processing units 111, 121 for the magnetic fieldtransmitting arrangement 110 and the magnetic field receivingarrangement 120, respectively.

Each air spring height measurement arrangement function (transmitter andreceiver) have their own, independent from each other running electroniccircuit. The electronic modules share the same power supply.

FIG. 17B illustrates separate power supply and separate signal conditionand processing units for the magnetic field transmitting arrangement andthe magnetic field receiving arrangement, respectively.

Each of the two different air spring height measurement arrangementfunctions (transmitter and receiver) has its own, independent from eachother, electrical power supply. Thus, there may be no need for a directwire connection between the two functions.

In this example (two different power supplies), it may be possible thatthe electric supply for the transmitter is self generated by one (or acombination) of the following means: battery (rechargeable ornone-rechargeable), vibration powered electric current generator (roadsurface dependent), acoustic sound powered generator (which is anotherform of vibration), electromagnetic energy transfer.

FIG. 17C illustrates a common power supply and a common signalprocessing unit comprising a transmitter circuit 111 and a receivercircuit 121 for the magnetic field transmitting arrangement and themagnetic field receiving arrangement.

In this example, the two air spring height measurement arrangementfunctions (transmitter and receiver) are placed onto one and the samePCB (Printed Circuit Board). In this case the entire electronics isrunning from the same power supply lines.

FIG. 18A illustrates a mounting plate 210 with the third coil 143attached to the mounting plate. The third coil generates the firstmagnetic field 181 for determining a distance to the magnetic fieldreceiving arrangement, which is not shown in this arrangement.

FIG. 18B illustrates a mounting plate 210 with the third coil 143 andtwo compensation coils 140 arranged at the front side and the back sideof the core of the third coil in order to adjust the direction and thestrength of the magnetic field lines of the first magnetic field 181such that a measuring direction or a working stroke may be larger. Thepolarity of the compensation coils 140 may be adapted to redirect themagnetic field lines of the first magnetic field 181 such that lessmagnetic flux enters the mounting plate 210 or is distracted by themounting plate 210.

When a mounting plate of the air spring height measurement arrangementfor mounting it on or in an air spring is tooled from or comprisesferromagnetic material (like magnetic steel) then the magnetic fieldgenerated and emitted by the transmitter coil may be absorbed to acertain extent. The closer the transmitter coil is placed to themounting plate, the more of the magnetic field will be absorbed that isgenerated by the transmitter coil 143. Consequently, the transmittingrange may be negatively interfered and may result in a shortermeasurement distance.

In a similar way the electromagnetic signal that has to be received bythe receiving coils 141, 142 may be affected when they are placed nearto a ferromagnetic mounting plate.

In other words, an active magnetic field deflecting design is used.Instead of allowing the magnetic flux to be absorbed by the mountingplate, for example a steel plate, additional coils, placed near to theend of the transmitter inductor will emit a magnetic field with thepolarity identical to the field coming out at the end of the coredevice.

Identical magnetic polarities repel each other and with this activelyreduce the number of magnetic flux lines that otherwise would choose totravel through the steel plate. Final consequence, the transmittingrange may be extended. On the other side, the complexity of thetransmitter circuit may be increased and so the electric currentconsumption.

In an alternative embodiment, the core of the third coil may be a bentor a buckled core such that the surface areas of the core are directedtowards the intended direction of the magnetic field.

FIG. 19 illustrates an air spring height measurement arrangement with anair coil as the third coil 143 and two cored coils as the first coil 141and the second coil 142, wherein the first and second coil are arrangedsymmetrical to a symmetry line 165, which may be the central axis of thethird coil 143 in one exemplary embodiment.

The central axes of the first and the second coil may be arrangedperpendicular to the symmetry line 165 or the central axis of the thirdcoil.

When placing cored receiving coils 141, 142 perpendicular to the centralaxis of the transmitting coil, the receiving coil (or the receivingcoils) may be placed “off-center” in relation to the transmitter aircoil. In case one perpendicularly placed cored receiver coil would beplaced right above the air coil center line or central axis of the thirdcoil, there may be no signal to measure as the magnetic field lines 181may cancel out each other inside the elongated receiver coil core.

FIG. 19 shows two receiver coils 141, 142 placed with a lateral offsetor off center in relation to the central axis of the transmitter aircoil 143. By building the differential signal of the two receiving coilsthis specific height/distance sensor design may achieve a very widesensing range. This design may be very sensitive to assembly tolerancesand shifts of the transmitter center line (which may happen when thevehicle movements cause a temporarily misalignment between the bottomand the top of the air spring, in case the air spring height measurementarrangement is mounted in or on an air spring.

This design may assure a large working stroke or a large measuringdistance as the receiver coils and the transmitter coils do not takeaway much “vertically” oriented space inside the air spring, i.e. thelongitudinal expansion of the cores of the first and second coils isperpendicular to the measuring distance from the third coil 143 to thefirst and second coil 141, 142.

This design may allow a differential signal (signal of the first coil141−signal of the second coil 142) and a very good compensation forunwanted EMI effects without the use of complex electronic circuits.

FIG. 20A illustrates a magnetic field receiving arrangement 120comprising three coils 140 which are arranged circular.

It should be noted that the magnetic field receiving arrangement as wellas the magnetic field transmitting arrangement as described above andhereinafter each may comprise one, two or more coils, wherein each ofthe coils may be inclined with respect to the intended measuringdirection or movement direction of the magnetic field transmittingarrangement or the magnetic field receiving arrangement.

FIG. 20B illustrates a mounting plate 210 having the magnetic fieldreceiving arrangement 120 illustrated in FIG. 20A, wherein the mountingplate has a circular recess in its center.

Three oval shaped or kidney shaped receiver coils or transmitter coilsmay allow triangulating the distance and the position of the transmittercoil or the receiver coil, respectively. With this, the exact positionof the Air-Springs top-and-bottom plates (in relation to each other) maybe determined and quantified in a three dimensional space (distance,left and right position: Z, X, and Y). When using a PCB coil design thenit may be even more easily to realize such multi coil design.

Of course, when using a four coil design, the determination (and withthis the computer algorithms required for calculation) may be muchsimpler to define the position of the transmitting (or receiving) coil.

FIG. 21A illustrates an air spring 300 with a first mounting element310, a second mounting element 320, and a bellow 330 extending from thefirst mounting element to the second mounting element and enclosing anair volume inside the air spring. The air spring 300 is adapted tochange is extension along the direction 130 and thus provide therequired spring effect. Within the air spring, a magnetic fieldtransmitting arrangement 110 and a mounting plate 210 with a magneticfield receiving arrangement (not shown) are installed in order tomeasure the distance between the magnetic field receiving arrangementand the magnetic field transmitting arrangement and thus the expansionor extension of the air spring.

FIG. 21B illustrates the air spring of FIG. 21A in a mounted state, i.e.with the magnetic field transmitting arrangement 110 and the mountingplate 210 with the magnetic field receiving arrangement within the airspring and in particular within the air volume of the air spring.

FIG. 22 illustrates a wheel suspension of a vehicle with two air springs300 as described above and hereinafter. The movable part 220, which ismounted to the wheel, is adapted to move along the arrows 130, whichcorrespond to the measuring distance 130 and moving direction 225 of theair springs, wherein one mounting element of the air spring is attachedto the movable part 220. The other one mounting part of the air springis mounted to the vehicle's chassis 230.

The air spring 300 as shown in FIG. 22 may in particular comprise an airspring height measurement arrangement as illustrated in one of the FIGS.1A to 12, as the moving direction of the air spring is in general alinear moving.

FIG. 23 illustrates an alternative wheel suspension of a vehicle withone air spring 300, wherein one mounting element of the air spring isattached to the movable part 220 and the other one mounting element isattached to the vehicle's chassis 230 and wherein the movable part isrotatably movable around the hinge 221.

The air spring 300 as shown in FIG. 23 may in particular comprise an airspring height measurement arrangement as illustrated for example inFIGS. 16 and 16A as the movable part and thus the mounting elementattached to the movable part performs a rotary movement or an arc shapedmovement.

In other words, depending on the mechanical design of the vehiclessuspension system, the axle of the vehicle is either moving up and down(as shown in FIG. 22) on a straight path, or the axle might follow anarc shaped path (as shown in FIG. 23). In the first incident the top andbottom plates of the air spring remain parallel to each other at alltimes, while in the second incident they do not remain parallel. Thismay have an implication on the air spring height measurement arrangementdesign as well.

In most cases the vehicles axles are mounted in such way that when thewheel is moving up and down (because of the road and drivingconditions), the wheel will execute this movement following one singleaxis like “straight up” or “straight down”. When related just to heightmeasurement, the potential side movement may be ignored for purposes ofbetter understanding. In such a case the used air spring(s) are alsocontracting and expanding following a straight line.

Particular in some trailer designs, the axle fixture is such that thewheel is moving up and down following an arc shaped curve, meaning thatthe contraction and expansion of the air spring is now following a twoaxial path. This means that the top and bottom plates of the air springare not in a parallel position when the air spring is expanding.

In applications where the air spring plates are not staying in aparallel position to each other, at least two receiver coils may beneeded to compensate for the effects of the non-linear sensor systemmovement. However, when using three or more than three receiver coilsthen “any” type of movement of the suspension system may be detected andmeasured including “side” movements. In most cases an air spring has amechanical buffer, or mechanical “stop” function built in the center ofthe top and bottom plates. This may prevent that the air spring may bedamaged in a fully deflated (fully contracted) position. Therefore, thecenter area of any coil design (this applies to magnetic fieldtransmitting arrangement and magnetic field receiving arrangement, i.e.to transmitter coils and to receiver coils, respectively) may have to bekept free.

This application claims benefit of European Patent Application SerialNo. EP 12191149, filed on Nov. 2, 2012. While certain representativeembodiments and details have been shown for the purpose of illustratingthe subject invention, it will be apparent to those skilled in this artthat various changes and modifications can be made therein withoutdeparting from the scope of the subject invention.

What is claimed is:
 1. An air spring height measurement arrangement,comprising a magnetic field transmitting arrangement; and a magneticfield receiving arrangement; wherein the magnetic field transmittingarrangement is adapted to adopt a first state and a second state withregard to the magnetic field receiving arrangement; wherein one of themagnetic field transmitting arrangement and the magnetic field receivingarrangement comprises a first coil and a second coil; wherein the otherone of the magnetic field transmitting arrangement and the magneticfield receiving arrangement comprises a third coil; wherein a firstcentral axis of the first coil and a second central axis of the secondcoil enclose a first angle which is unequal to 0°; and wherein, in thefirst state, a third central axis of the third coil and the firstcentral axis enclose a second angle which is unequal to 0°.
 2. The airspring height measurement arrangement according to claim 1, wherein themagnetic field transmitting arrangement comprises a magnetic fieldreceiving unit and the magnetic field receiving arrangement comprises amagnetic field transmitting unit; wherein the magnetic fieldtransmitting arrangement is adapted to transmit a first magnetic field;wherein the magnetic field receiving arrangement is adapted to receivethe first magnetic field; wherein the transmitting unit is adapted totransmit a second magnetic field which is generated out of an energycorresponding to the received first magnetic field; and wherein thereceiving unit is adapted to receive the second magnetic field.
 3. Theair spring height measurement arrangement according to claim 1, whereinthe first angle is equal to the second angle.
 4. The air spring heightmeasurement arrangement according to claim 1, wherein at least one ofthe first coil, the second coil, and the third coil comprises a coreelement.
 5. The air spring height measurement arrangement according toclaim 1, wherein, in the first state, the third central axis and thesecond central axis run parallel to each other.
 6. The air spring heightmeasurement arrangement according to claim 1, wherein, in the firststate, the third central axis and the second central axis coincide. 7.The air spring height measurement arrangement according to claim 1,wherein the first coil comprises a lateral offset in a directionperpendicular to the first central axis with regard to the second coil.8. The air spring height measurement arrangement according to claim 1,wherein the first coil overlaps the second coil in an overlap section atleast partially in a direction perpendicular to the first central axis.9. The air spring height measurement arrangement according to claim 8,wherein the first coil completely overlaps the second coil in adirection perpendicular to the first central axis.
 10. The air springheight measurement arrangement according to claim 1, wherein the thirdcoil is adapted to move along the first central axis when being movedfrom the first state to the second state.
 11. The air spring heightmeasurement arrangement according to claim 1, wherein each of the firstcoil and the second coil is a printed coil on a printed circuit board.12. The air spring height measurement arrangement according to claim 1,wherein in the second state, the third central axis and the firstcentral axis run parallel to each other.
 13. The air spring heightmeasurement arrangement according to claim 1, wherein, in the firststate, the third coil and the second coil are arranged opposite to eachother in a direction of a second measuring direction.
 14. The air springheight measurement arrangement according to claim 13, wherein, in thesecond state, the third coil and the first coil are arranged opposite toeach other in a direction of a first measuring direction.
 15. The airspring height measurement arrangement according to claim 14, wherein amovement of the magnetic field transmitting arrangement from the firststate to the second state is adapted to occur within a measuring planewhich is defined by the first measuring direction and the secondmeasuring direction.
 16. An air spring for a vehicle, comprising a firstmounting element for being fixed to one of a vehicle's chassis and amovable part of a vehicle being movable with respect to the chassis; asecond mounting element for being fixed to the other one of thevehicle's chassis and the movable part of the vehicle being movable withrespect to the chassis; a bellow extending from the first mountingelement to the second mounting element and including an air volume; anair spring height measurement arrangement according to claim 1; whereinthe magnetic field transmitting arrangement is arranged at the firstmounting element; wherein the magnetic field receiving arrangement isarranged at the second mounting element; and wherein a movement of thefirst mounting element with respect to the second mounting elementrepresents at least a part of a working stroke of the air spring. 17.The air spring for a vehicle according to claim 16, wherein the magneticfield transmitting arrangement comprises a magnetic field receiving unitand the magnetic field receiving arrangement comprises a magnetic fieldtransmitting unit; wherein the magnetic field transmitting arrangementis adapted to transmit a first magnetic field; wherein the magneticfield receiving arrangement is adapted to receive the first magneticfield; wherein the transmitting unit is adapted to transmit a secondmagnetic field which is generated out of an energy corresponding to thereceived first magnetic field; and wherein the receiving unit is adaptedto receive the second magnetic field.
 18. The air spring for a vehicleaccording to claim 16, wherein the first angle is equal to the secondangle.
 19. The air spring for a vehicle according to claim 16, whereinat least one of the first coil, the second coil, and the third coilcomprises a core element.
 20. The air spring for a vehicle according toclaim 16, wherein, in the first state, the third central axis and thesecond central axis run parallel to each other.